The modified Global Assessment of Functioning (GAF) scale has more detailed criteria and a more structured scoring system than the original GAF. The two scales were compared for reliability and validity. Raters who had different training levels assigned hospital admission and discharge GAF scores from patient charts. Intraclass correlation coefficients for admission GAF scores were higher for raters who used the modified GAF (0.81), compared with raters who used the original GAF (0.62). Validity studies showed a high correlation (0.80) between the two sets of scores. The modified GAF also correlated well with Zung Depression scores (-0.73). The modified GAF may be particularly useful when interrater reliability needs to be maximum and/or when persons with varying skills and employment backgrounds--and without much GAF training--must rate patients. Because of the increased structure, the modified GAF may also be more resistant to rater bias.